1. Field of the Invention
The present invention relates generally to motor control devices and motor control methods. More specifically, the present invention relates to motor control devices and motor control methods driving without using a sensor a synchronous motor having a plurality of phase windings and used for example for compressors of air conditioners.
2. Description of the Background Art
In recent years, environmental issues have become social issues and energy-saving has become an important issue. In particular, in the field of motors there is an acute need for a small, high-efficiency, high-output motor to save energy, while there has also been provided a motor distinguished in configuration from conventional motors.
FIG. 45 shows a representative configuration of a conventional motor with a rotor and a stator cut in half and thus shown in a 1/2 model. In FIG. 45, rotor 121 is provided in the form of a column formed of a stacked steel plates. Rotor 121 is provided at an outer circumference thereof with a permanent magnet 122 arranged with its N pole and S pole alternate circumferencially. Permanent magnet 122 has an outer peripheral surface having fixed thereto a non-magnetic SUS tube 123 to prevent the magnet from scattering while it rotates. Stator 125 is provided with a plurality of protruding poles 126 extending radially. Between protruding poles 126 is formed a slot 127 with a coil (not shown) wound therearound.
This motor is a surface permanent magnet (SPM) motor employing a Fleming torque according to Fleming""s rules attributed to a magnetic field created by permanent magnet 122 and a coil current (not shown). It is significantly suitable for mass production.
To enhance efficiency, however, an interior permanent magnet (IPM) motor is also noted. This motor has a permanent magnet embedded in its rotor to employ a reluctance torque in addition to a Fleming torque.
FIG. 46 shows an exemplary configuration of an IPM motor. As shown in FIG. 46, the IPM motor includes a rotor 130 with a permanent magnet 132 embedded in a rotor core 131 in the form of a circular column formed of a highly permeable iron core or stacked silicone steel plates. FIG. 46 shows a 4-pole motor, with 4-pole permanent magnet 132 arranged in rotor 130, with their N and S poles alternate circumferencially, although in FIG. 46 the four poles are shown in a 1/2 model. Rotor core 131 is circumferentially provided with a stator 135 having a protruding pole 136.
Such configuration provides a difference between an inductance Ld along an axis d corresponding to a direction extending between the center of permanent magnet 132 and that of rotor 131 and an inductance Lq along an axis q corresponding a direction rotated relative to axis d by an electrical angle of 90xc2x0, and in addition to a Fleming torque caused by permanent magnet 132 a reluctance torque is also caused. Such relationship, as described in Rotary Machines Employing Reluctance Torque, Nobuyuki Matsui et al, T. EEE Japan Vol.114-D, No.9, 1994, is provided by the following expression (1):
T=Pnxc3x97xcfx86axc3x97iq+Pnxc3x971/2xc3x97(Ldxe2x88x92Lq)xc3x97idxc3x97iqxe2x80x83xe2x80x83(1)
wherein
Pn: the number of pole pairs
xcfx86a: interlinkage flux
Ld: inductance along axis d
Lq: inductance along axis q
id: current along axis d
iq: current along axis q
The FIG. 45 SPM motor has a permanent magnet substantially equal in permeability to air. Thus, in expression (1) both inductances Ld and Lq have substantially the same value and in expression (1) at the second item no reluctance torque is caused. In the FIG. 46 IPM motor, however, the inductance along axis d is a direction in which a magnetic flux of the permanent magnet is caused, and the flux along axis d flows through the permanent magnet, which is substantially equal in permeability to air. This would result in an increased magnetic resistance and a reduced inductance Ld along axis d.
In contrast, the inductance along axis q passes through a gap of the permanent magnet, which results in a reduced magnetic resistance and an increased inductance Lq along axis q. Thus, there would be introduced a difference between inductance Ld along axis d and inductance Lq along axis q and passing a current Id along axis d would cause a reluctance torque in expression (1) at the second item.
If the above relationship is seen in terms of flux vector, a Fleming torque Tm is caused by multiplying a magnetic flux xcfx86a by a current Iq flowing in a direction electrically orthogonal. Similarly, a reluctance torque Tr is provided by fluxes Ldxc2x7Id and Lqxc2x7Iq attributed to inductance and current come by electrically orthogonal currents Id and Iq, respectively. These two torques added together correspond to a total torque Tt.
This total torque varies with a current phase xcex2 input. Herein current phase xcex2 is an representation in electrical angle of a phase of a motor current relative to a positional relationship between the permanent magnet and the coil. If this is considered in expression (1) then an expression (2) is provided:
Tt=Pnxc3x97xcfx86axc3x97iaxc3x97cos xcex2+Pnxc3x971/2xc3x97(Ldxe2x88x92Lq)xc3x97ia2xc3x97sin 2xcex2xe2x80x83xe2x80x83(2)
wherein,
Pn: the number of pole pairs
xcfx86a: interlinkage flux
Ld: inductance along axis d
Lq: inductance along axis q
id: current along axis d
iq: current along axis q
xcex2: current phase
ia: magnitude of current vector
FIG. 47 represents a relationship between Fleming torque Tm and reluctance torque Tr and the summation thereof or total torque Tt with current phase xcex2 varied. Herein, when the center of the permanent magnet is located at that of the coil (e.g., that of the coil at a phase windings U, the winding""s current phase is 90xc2x0. Fleming torque Tm is maximized for a current phase of 90xc2x0. As the current phase advances Fleming torque Tm is reduced, and for a current phase of 180xc2x0 it reaches zero.
In contrast, reluctance torque Tr is maximized for a current phase of 135xc2x0. As such, the summation of the both torques or total torque Tt, although varying depending on their respective torque ratios, is maximized for a current phase of approximately 115xc2x0, as shown in FIG. 47 by a solid line. As such, if an IPM motor""s current is equal to an SPM motor""s current, the IPM motor, which effectively uses a reluctance torque, can provide an output with a higher torque than the SPM motor, which only employs a Fleming torque.
The magnitude of a torque is determined depending on various factors, among which is also important is a current drive method.
FIGS. 48A-48D are waveform diagrams showing one example of 120xc2x0 rectangular-wave drive corresponding to a conventional current drive method. FIGS. 48A, 48B and 48C represent their respective current waveforms of phase windings U, V, W, respectively. As shown in FIGS. 48A-48C, in the current drive method an inverter is controlled to link current conductions of two of three phase windings (U, V, W) for each 120xc2x0 to provide a direct current. It can be seen that for each phase winding there is provided a pause period, during which an induced voltage caused at a stator coil as a rotor magnet rotates is detected to control the rotor""s rotation.
For an IPM motor employing a reluctance torque, as described above, controlling a timing of conduction is an important factor in obtaining a maximized torque, and conventionally a rotor phase can only be detected by a 120xc2x0 rectangular-wave drive method employing an induced voltage to detect the rotor phase. This method, however, has a pause period for detecting the induced voltage and is thus disadvantageous in terms of motor efficiency, oscillation and noise.
To overcome such disadvantages, a method has been proposed as described in International Publication No. WO95/27328. In this method, a motor has a permanent magnet embedded therein, with a conduction width set to correspond to an electrical angle of 180xc2x0, and a magnetic pole is positionally detected depending on a difference between a potential of a first neutral point of the motor""s coil and that of a second neutral point attributed to a bridge circuit in electrically parallel with the coil.
FIG. 49 is a block diagram showing a configuration of a brushless DC motor drive control device allowing a 120xc2x0 conduction. As shown in FIG. 49, between terminals of a direct current power supply 211 three pairs of switching transistors 212u, 212v, 212w are each connected in series to configure an inverter and a voltage of a point connecting each pair of transistors together is applied to brushless DC motor 213 at the respective one of Y-connected windings 213u, 213v, 213w of a stator and also at the respective one of Y-connected resistors 214u, 214v, 214w. 
Furthermore, stator windings 213u, 213v, 213w have therebetween a neutral point 213d connected to an interconnection 213e, and resistors 214u, 214v, 214w have therebetween a neutral point 214d connected to interconnection 214e. The neutral point 213d voltage is fed via a resistor 215a to an amplifier 215 at an inverted input terminal, and the neutral point 214d voltage is transparently fed to amplifier 215 at a non-inverted input terminal. Between the amplifier 215 output terminal and non-inverted input terminal a resistor 215b is connected to allow amplifier 215 to operate as a differential amplifier.
Herein, the neutral point 213d voltage En0 is a sum of a waveform of an output from the inverter and a 3n-order harmonic component included in a waveform of an induced voltage of the motor, wherein n represents an integer. In contrast, the neutral point 214d voltage only corresponds to the waveform of an output from the inverter. Thus, the 3n-order harmonic component can be extracted by obtaining the difference between the neutral point 213d voltage and the neutral point 214d voltages. As such, a waveform of an induced voltage of the motor or a position of the rotor can be detected without employing a magnetic-pole position sensor.
The above-described conventional example, however, also has a setback as described below: more specifically, a magnet-embedded IPM motor is most efficiently operated with an optimal current condition phase angle advance. In setting such advance, detecting a phase of a rotor relative to a stator is an important factor. Accordingly, International Publication No. WO95/27328 discloses that, with a 180xc2x0 sine-wave conduction applied, there are provided an interconnection for outputting a neutral-point voltage from a motor coil connection, an interconnection for outputting a neutral-point voltage from a resistor connection 14u, 14v, 14w, and a differential amplifier and other external circuits and additional circuits, to allow the rotor""s phase to be detected. However, it requires interconnections, a discriminator and detector circuit, resistors, and other components for detection, which would increase the number of components and the cost thereof. In particular, an interconnection providing neutral point 13d from a motor coil connection is disadvantageous, since it requires that the motor configuration and the terminal configuration be changed and thus not applicable to conventional motors.
The conventional system is also disadvantageous as it is hard to control; with a 180xc2x0 sine-wave conduction applied, a voltage induced by a magnet and a magnetic flux with a reluctance torque generated would cause a phase difference between an applied voltage and a coil terminal current and the efficiency characteristic of the applied voltage relative to the conduction phase id steeper than when a 120xc2x0 conduction is applied. As such, inaccurate phase control would disadvantageously result in efficiency varying significantly.
A main object of the present invention therefore is to provide a motor control device and method capable of reducing the number of components to reduce the cost therefor and reliably controlling a motor.
Another object of the present invention is to provide a motor control device and method capable of readily and accurately detecting phase difference information to drive a synchronous motor with reduced noise, reduced oscillation and increased efficiency.
Still another object of the present invention is to provide a motor control device and method capable of detecting a motor current area in a simplified manner and thus at low cost and also with high precision.
The present invention provides a motor start control device controlling a synchronous motor, including motor current detection means detecting a motor current flowing through a coil of the synchronous motor, detection means detecting information of a phase difference between the motor current and a drive voltage supplied to the coil, and control means referring to the phase difference information to detect the current condition of the synchronous motor and referring to the condition of the synchronous motor to control the drive voltage applied to a terminal of the coil and a frequency of a conduction to the terminal of the coil.
Thus, in the present invention, a phase difference between a motor drive voltage and a motor current may be referred to to detect the current condition of the motor""s rotation to start and drive the motor. Furthermore, phase difference information may be referred to to detect whether the synchronous motor has been completely started and thus rotates in stable manner. As such, the motor can be reliably, completely started in a sensorless system without a motor position detector and thus does not fail to start and thus rotates in stable manner. Adopting a sensorless system can eliminate a position detector and thus save the cost therefor.
The present invention provides preferable embodiments, as described below:
Phase difference information may be obtained by calculating an area of a motor current waveform in a predetermined phase period of a drive voltage waveform to facilitate calculating a phase difference. Since an area of a motor current is used to detect phase difference information, the present invention is more resistant to noise than edge detection, such as zero-cross detection, and without being affected by an oscillation of the motor current can reliably detect phase difference information. As such, the motor can be free of erroneous operation and completely started and thus rotates in stable manner.
Furthermore, phase difference information may be obtained by calculating a ratio between a first area of a motor current waveform in a first predetermined phase period of a drive voltage waveform and a second area of the motor current waveform in a second predetermined phase period of the drive voltage phase. Thus a phase difference can be accurately and readily calculated. Since an area of a motor current may be used to detect phase difference information, the present invention is more resistant to noise than an edge detection method, such as zero-cross detection, and without being affected by an oscillation of the motor current can reliably detect phase difference information. As such, the motor can be free of erroneous operation and completely started and thus rotate in stable manner.
Furthermore, an area of a motor current can be calculated by accumulating values obtained by analog-digital (A-D) sampling the motor current in a predetermined phase period at predetermined intervals. As such, the area can be calculated with a simple circuit configuration. Thus a control system can be simply configured to reduce the cost therefor.
Furthermore, the first area may be an accumulation of values obtained by A-D sampling a current motor in the first predetermined phase period at predetermined intervals, and the second area may be an accumulation of values obtained by A-D sampling the motor current in the second predetermined phase period at predetermined intervals. As such, a simple circuit configuration may be used to sample the motor current and thus calculate such areas and further to calculate a ratio thereof. As such, a control system can be simply configured to reduce the cost therefor.
Furthermore, the control means may refer to a variation of phase difference information to detect that the synchronous motor has been completely started and thus rotates in stable manner. As such, the present invention does not require a sensorless system to detect an unstable rotation state associated with a varying phase difference, while the control means may refer to a variation of a phase difference in a sensorless system to reliably detect that the motor has been completely started. As such, the motor does not fail to start and thus rotates in stable manner.
Furthermore, the control means may refer to a variation of phase difference information to detect that the synchronous motor is rotating in unstable manner and in response to the detection of the unstable rotation state the control means may refer to a variation of phase difference information to detect that the synchronous motor has been completely started and thus rotates in stable manner. Thus, the control means can reliably detect that the motor has been completely started (or is rotating in stable manner) after it rotates in unstable manner. As such, the motor does not fail to start and the control means can more reliably determine as to whether the motor has been completely started. That is, the motor control device can be enhanced in reliability.
Phase difference has a limited variation when the synchronous motor has been completely started and thus rotates in stable manner, and the control means may also compare a variation of phase difference information with a predetermined value to detect that the synchronous motor has been completely started and thus rotates in stable manner so as to precisely detect that the motor has been completely started and thus rotates in stable manner.
Furthermore, the control means may compare a variation of phase difference information with a first predetermined value to detect that the motor is rotating in unstable manner and the control means may compare a variation of phase difference information with a second predetermined value to detect that the synchronous motor has been completely started and thus rotates in stable manner. The control means can precisely detect an unstable rotation state with a phase difference having a large variation and thereafter a stable rotation state with a phase difference having a limited variation, i.e., that the motor has been completely started.
Furthermore, from the start of starting the synchronous motor until the motor has been completely started and thus rotates in stable manner, the control means may maintain a conduction frequency of a predetermined value while varying a reference duty value of a drive voltage with time. By varying a reference duty value the synchronous motor can transition rapidly and thus be completely started rapidly (or rotate in stable manner) to reduce the time required for completely starting the motor. Furthermore, the control means can detect that the motor rotates in unstable manner and then that the motor has been completely started (or rotates in stable manner). As such the motor does not fail to start.
Furthermore, from the start of starting the synchronous motor until the motor has been completely started and thus rotates in stable manner, the control means may maintain a drive voltage of a predetermined value while varying a conduction frequency with time. By varying a conduction frequency the motor can transition rapidly and thus be completely started rapidly and thus rotate in stable manner to reduce the time required for completely starting the motor. Furthermore, the control means can detect that the motor rotates in unstable manner and then that the motor has been completely started (and rotates in stable manner). As such, the motor does not fail to start.
Furthermore, from the start of starting the synchronous motor until the motor has been completely started and thus rotates in stable manner, the control means sets a conduction frequency and a drive voltage each to a value corresponding to the synchronous motor having been completely started and thus rotating in stable manner. Thus, the motor can transition rapidly and thus be completely started rapidly and thus rotate in stable manner to reduce the time required for completely starting the motor. Furthermore, the control means may detect that the motor rotates in unstable manner and then that the motor has been completely started (and thus rotates in stable manner). As such the motor does not fail to start.
Furthermore, in starting the synchronous motor the control means may refer to a variation of phase difference information to set an amount in variation of a reference duty value of a drive voltage. Since the control means may refer to a variation of phase difference information to vary a reference duty value, the motor can transition rapidly and thus be completely started rapidly and thus rotate in stable manner to reduce the time required for completely starting the motor. Furthermore, referring to a variation of a phase difference and thus setting an amount in variation of a reference duty value of a drive voltage, also allows the motor to rapidly transition through a condition often associated with oscillation or stepping-out. As such the motor can be increased in longevity and its peripherals can be enhanced in reliability.
Furthermore, in starting the synchronous motor the control means may refer to the current condition of the synchronous motor to set an amount in variation of a reference duty value of a drive voltage. As such, the motor can transition rapidly and thus be completely started rapidly and thus rotate in stable manner to reduce the time required for completely starting the motor. Furthermore, the motor can rapidly transition through a condition oftentimes associated with oscillation or stepping-out. As such, the motor can be increased in longevity and its peripherals can be enhanced in reliability.
Furthermore, the control means may limit to a value a reference duty value of a drive voltage. Limiting a PWM duty value can prevent the value from being increased to too large a value to allow an excessive current to flow through an inverter and the motor and damage them. As such, the device can be enhanced in reliability.
Furthermore, in starting the synchronous motor the control means may refer to a variation of phase difference information to set an amount in variation of a conduction frequency. Referring to a variation of phase difference information to vary a conduction frequency allows the motor to transition rapidly and thus be completely started rapidly and thus rotate in stable manner so as to reduce the time required for completely starting the motor. Furthermore, the motor can rapidly transition through a condition oftentimes associated with oscillation or stepping-out. As such the motor can be increased in longevity and its peripherals can be enhanced in reliability.
Furthermore, in starting the synchronous motor the control means may refer to a condition of the synchronous motor to set an amount in variation of a conduction frequency. Varying a conduction frequency allows the motor to transition rapidly and thus be completely started rapidly and thus rotate in stable manner so as to reduce the time required for completely starting the motor. Furthermore, the motor can rapidly transition through a condition oftentimes associated with oscillation or stepping-out. As such the motor can be increased in longevity and its peripherals an be enhanced in reliability.
Furthermore, after the control means has detected that the synchronous motor has been completely started and thus rotates in stable manner, the control means drives the synchronous motor to allow phase difference information to have a predetermined value. Driving the motor in the normal operation under phase difference control does not entail changing a method of detecting phase difference information to another. This eliminates the necessity of switching an operation method for example from a synchronous operation to start the motor to an counter-electromotive operation in the normal operation, as conventional. As such, the synchronous motor can smoothly transition from its starting condition to its normal operation. Thus, torque variation, noise and oscillation can be reduced and the motor can also be prevented from stopping when its operation method would otherwise fail to switch successfully. Since it is not necessary to switch the currently applied method of detecting phase difference information, a control system can have its burden reduced to further reduce the cost therefor.
Furthermore, after the control means has detected that the synchronous motor has been completely started and thus rotates in stable manner, the control means may increase a rotation rate of the synchronous motor to a rotation rate allowing a counter-electromotive force to be detected in a coil of the motor and the control means may refer to the counter-electromotive force to switch conduction to drive the synchronous motor. While the synchronous motor is being started it may be driven with reference to a phase difference, and when it normally operates it may be driven with reference to a counter-electromotive voltage. Thus the motor can be reliably started, and referring a counter-electromotive force in the normal operation to switch conduction allows a simple configuration to be used to provide a control system.
Furthermore, at least in starting the synchronous motor the control means drives the motor with 180xc2x0 conduction. The motor can be started without a conduction pause period introduced in a motor drive waveform, such as when 120xc2x0 rectangular-waveform is applied, to detect a counter-electromotive force. As such, torque variation, noise, oscillation and the like can be reduced to start the motor smoothly. Furthermore, a magnet flux can be effectively used to achieve high efficiency.
The present invention in another aspect provides a device controlling a motor with a rotor having a magnet embedded therein, employing a reluctance torque to rotate the rotor, including: current detection means for detecting a current flowing through a coil of the motor to output current phase information; means for setting information of a phase of a voltage applied to the coil; compare means for comparing the current phase information output from the current detection means with the voltage phase information set by the means for setting, to detect a difference between the phases; reference phase difference value storage means previously storing a desired reference phase difference value; and drive means for driving the motor to allow a difference between the phase difference detected by the compare means and the reference phase difference value stored in the reference phase difference value storage means, i.e., phase difference information to attain a desired value.
Thus, in the present invention, without a change introduced into its configuration the motor can be applied to conventional motors and also superior in controllablity.
The present invention provides preferable embodiments, as follows:
Phase information setting means includes means for setting a rotation rate of a motor, a sine wave table previously storing sine wave data corresponding to a rotation rate, and a sine wave data creation means referring to a set rotation rate to read corresponding sine wave data from the sine wave table, and outputting information of a phase of a voltage applied to a coil. The drive means includes pulse width modulated (PWM signal generation means referring to phase difference information corresponding to a difference between a phase difference detected by the compare means and a reference phase difference value stored in the reference phase difference value storage means and to sine wave data output from the sine wave data creation means, for generating a PWM signal for each phase winding, and inverter means including a switching element provided for each phase winding, referring to a PWM signal generated by the PWM signal generation means, for switching a corresponding switching element.
Furthermore, a current through the motor coil and a voltage applied to the motor coil has therebetween a phase difference of zero, and the motor coil voltage has a conduction width corresponding to an electrical angle of 180xc2x0 and has a conduction waveform selected to be a sine wave.
The present invention in still another aspect provides a motor control device driving and controlling a synchronous motor having a motor coil with a plurality of phase windings, including: drive-wave data creation means responsive to issuance of an instruction to set a rotation rate for creating drive-wave data used to drive the synchronous motor for each of the plurality of phase windings; motor current detection means for detecting a motor current of any specific one of the plurality of phase windings to output a motor current signal; phase difference detection means for detecting a motor drive voltage phase of a specific phase winding from drive wave data created by the drive wave data creation means, and detecting a phase difference between the motor drive voltage phase of the specific phase winding and a motor current signal output from the motor current detection means, to output phase difference information; phase difference control means for calculating a reference duty value used to control phase difference information output from the phase difference detection means to have a target value; duty calculation means for multiplying drive wave data for each phase winding output from the drive wave data creation means by a reference duty value output from the phase difference control means, to calculate an output duty for each phase winding; inverter means including a plurality of switching elements, responsive to a calculated output duty for each phase winding for generating a PWM signal to control conduction of each switching element to provide conduction through each motor coil, wherein the phase difference detection means obtains a motor current signal area of each of two phase periods with reference to a motor drive voltage phase of any specific phase winding and calculates the ratio of the motor current signal areas of the two phase periods and provides the area ratio as phase difference information.
Thus, in the present invention, in driving the synchronous motor a sine wave can effectively achieve characteristics of 180xc2x0 conduction, i.e., reduced noise, reduced oscillation, high efficiency, and reduced power consumption.
Furthermore, the present invention can prevent phase difference information from being affected e.g. by noise and thus erroneously detected. As such, the phase difference information can be obtained accurately. Furthermore, if a phase of zero, which is hard to detect with zero-cross, is associated with a flat current waveform, phase difference information can be obtained accurately. Furthermore, the present invention can prevent the erroneous detection of phase difference information that is attributed to a variation of a low frequency component superimposed on a motor current. Thus, phase difference information can be obtained accurately.
Thus, even in disadvantageous, e.g., noisy environment or even with different rotation rates, phase difference control can be achieved with high precision. It is not necessary to provide a current sensor used to detect a current that is in particular provided internal to the motor; it may be accommodated in a motor control substrate. As such, interconnections may readily be provided and circuits can readily be designed. Furthermore, in the present invention, a motor current phase may be obtained from an area obtained by accumulating results of sampling a motor current, rather than from an edge such as zero-cross. As such, phase difference information can be detected accurately.
The present invention provides embodiments, as follows:
The phase difference detection means samples n times a motor current signal flowing through each of two phase periods with reference to a motor drive voltage, n being an integer no less than one, and accumulates each current sample data for output as a motor current signal area.
Furthermore, the phase difference detection means samples a motor current signal at equal intervals for a phase period with reference to a motor drive voltage phase. The phase difference detection means refers to a rotation rate to set a sampling interval. As such, a motor current can be sampled at timing designed through a calculation simplified. As such, a controlling microcomputer can provide its processing in a reduced period of time. Thus, rapid and precision phase-difference control can be achieved. Furthermore, an inexpensive controlling microcomputer may be used to achieve a cost reduction.
Furthermore, since the sampling rate n may be set depending on the rotation rate, a phase difference can be detected in accordance with the processing rate of the controlling microcomputer. As such, any controlling microcomputer can achieve its best performance in accordance with its ability. Furthermore, if an inexpensive controlling microcomputer is used, accurate phase-difference control can still be achieved and a cost reduction can thus be achieved. Furthermore, the controlling microcomputer does not overflow in the number of process steps. As such, high-precision phase difference control can be achieved.
Furthermore, two phase periods with reference to a motor drive voltage phase are a first period selected corresponding to a 0xc2x0-90xc2x0 period of the motor drive voltage phase and a second period selected corresponding to a 90xc2x0-180xc2x0 period of the motor drive voltage phase, or a first period selected corresponding to a 180xc2x0-270xc2x0 period of the motor drive voltage phase and a second period selected corresponding to a 270xc2x0-3601xc2x0 period of the motor drive voltage phase. Thus, the two phase periods are symmetrical in phase and their phase difference has a value with one as the center. As such, control-designing can be facilitated and the controlling microcomputer""s processing can be alleviated. Thus, rapid and high-precision phase difference control can be achieved. Furthermore, an inexpensive controlling microcomputer may be used and a cost reduction can thus be achieved.
Furthermore, after two phase periods starts with reference to a motor drive voltage phase, a first motor current sampling operation starts at a timing set by correcting an amount of drive-wave data exceeding a reference phase of drive-wave data of a specific phase winding. As such, an accurate motor voltage phase can be obtained. Thus accurate phase difference information can be detected and high-precision phase difference control can be achieved.
Furthermore, phase difference information may be obtained by averaging m ratios of motor current signal areas, m being an integer no less than one. Thus, accurate phase difference information can be obtained. As such, high-precision phase difference control can be achieved if the motor is in a poor, for example noisy environment, at a rotation rate with a motor current waveform distorting and varying significantly.
Furthermore, phase difference information may be obtained depending on an averaging frequency m set depending on the current rotation rate. As such, phase difference information can be detected according to a control band range as required and a phase difference information error as desired. Thus, stable phase-difference control can be achieved ensuring a controlling band range and a phase difference information error as desired.
Furthermore, the phase difference control means corresponds to a proportional and integral control operation on error data between phase difference information and target phase difference information. Since phase difference control may be provided through the PI control operation, residual error data existing in phase difference information can be converged at zero. Thus, phase difference control can be provided with high precision, matching a target phase difference. Furthermore, efficient phase difference control can be achieved.
Furthermore, the phase difference control means may set a control gain depending on a condition for the motor""s rotation or on target phase difference information. As such, if a condition for the motor""s rotation causes a difference in a phase-difference characteristic or a non-linearity more or less appearing in a phase-difference characteristic, they still can be compensated for. As such, in any conditions optimal phase-difference control can be achieved. As such, the motor can be driven efficiently to reduce power consumption.
Furthermore, target phase difference information may be set to an optimal value depending on a condition for the motor""s rotation. Since target phase difference information may be set depending on the rotation rate, a phase difference can be constantly tracked for that, varying depending on the rotation rate, can achieve maximized efficiency. Furthermore, there can also be eliminated an error between the motor current signal areas of two motor voltage phase periods that is attributed to an effect of a distortion of a motor current waveform. As such, under any rotating condition, the motor can be driven most efficiently and its power consumption can thus be reduced.
Furthermore, after two phase periods have completed with reference to one motor drive voltage phase, there may be provided a time period for calculating a ratio of motor current signal areas and averaging obtained area ratios to obtain phase difference information while the phase difference detection process is not performed. Since there may be provided a time period for an operation to detect phase difference information, target phase difference information may be set depending on the rotation rate and a phase difference can be constantly tracked for that, varying with the rotation rate, can achieve maximized efficiency. As such, under any rotating condition, the motor can be driven most efficiently and its power consumption can thus be reduced.
Furthermore, at least the phase difference detection means may provide its processing in a main loop of a process routine of a controlling microcomputer. As such, its processing would not be affected by any interrupt time. As such, if a slow-processing, inexpensive controlling microcomputer is used, accurate phase-difference control still can be achieved. Furthermore, a cost reduction can be achieved.
When a drive wave is set to allow a sine waveform or a current waveform to be substantially identical in waveform to a rotor magnet flux waveform, a more effective torque can be created to achieve high efficiency or reduce a conduction pause period. Furthermore the present invention may dispense with a position detection sensor to achieve a cost reduction.
Furthermore, a control gain may be set depending on an offset value set by the motor current detection means or a motor current signal amplitude value. As such, a phase difference control gain can be constantly set to an optimal value to achieve high-precision controllability to drive the motor in stable manner.
Furthermore, target phase difference information or a method of calculating phase difference information may be set with reference to a motor drive voltage phase. As such, phase difference information can be detected in a reduced period to allow the motor""s behavior to be detected more elaborately, and precision phase-difference control can also be achieved to drive the motor in more stable manner and more reliably.
Furthermore, the present invention in another aspect provides a method of controlling a motor having a rotor with a magnet embedded therein, and employing a reluctance torque to rotate the rotor, wherein a current flowing through a coil of the motor is detected to output current phase information and there also be set information of a phase of a voltage applied to the coil of the motor, the output current phase information is compared with the set information of the phase of the voltage applied to the coil to detect a phase difference, and the motor is driven to allow a difference between the detected phase difference and a previously stored reference phase-difference value, i.e., phase difference information to attain a desired value. Thus, without a change in its configuration the motor can be applied to conventional motors and it is also superior in controllability. More specifically, as is apparent from a result of an experiment using an IPM motor with a fixed rotation rate and a fixed load torque to examine an efficiency characteristic with respect to an applied voltage and a voltage-current phase difference, the present invention exhibits less steep an efficiency characteristic than a conventional example. Thus, the present invention can effectively provide a wider tolerable range in setting an optimal phase angle to obtain maximized frequency, and if the phase angle varies slightly, efficiency varies less frequently.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.